We will design an objective test, based on the Visual Evoked Potential (VEP), to measure amblyopic suppression. Our basic tool is the VEP monocular response to periodic vernier onset/offset transitions in bar stimuli, and its suppression during dichoptic stimulation with matching contours. What is unique about this approach is that it identifies which eye is being suppressed as well as the visual acuity of each eye. Although we will develop and validate this test in adult subjects, our dichoptic visual display system has been specifically designed for ultimate use with infants and pre-verbal children. We also will use a new multi-channel recording system (Geodesic Sensor Net) to explore the neural basis for the differences between normal and abnormal binocular processing. About 4% of all children suffer from strabismus and/or anisometropia during early development. These abnormalities place an individual at risk for a variety of visual deficiencies. The most serious outcome is amblyopia in one eye. Amblyopia refers to a loss of visual acuity, without obvious organic cause, that cannot be corrected by wearing spectacles or contact lenses. Perhaps one third of strabismics and anisometropes suffer some loss in visual acuity. The proposed test could assist with the diagnosis of amblyopia in infancy, as well as in monitoring progress during treatment, thereby improving the chance of a favorable outcome.